212 Ebola messages in my mailbox...

[Francisco Muril Zerbini]

Patrick O'Neil (patrick at corona) wrote:


: On 14 May 1995, Jane E. Hawkins wrote:

: > 
: > Question: The dim recesses of my memory say the the index cases for the 
: > last two Ebola outbreaks both worked in cotton mills. I recall one such 
: > mill being virtually pulled to pieces in an attempt to find an insect, 
: > animal, or any organic matter with traces of the virus, to no avail.

That would be Marburg, not Ebola. But your point is valid, since Marburg 
is closely related to Ebola and its natural host is also unknown.

:  I read of that and now wonder if they really did attempt to locate some 
: sort of animal or insect-borne host and exclude plants.  I wonder at the 
: possibility that ebola might reside in plants.  Just brainstorming, and I 
: can envision problems for a virus to hop from the physiological 
: environment of a plant to the completely different environment of an 
: animal, especially since we have active immune systems of a nature far 
: different than a plant...

: Patrick

You know, I have entertained the idea that Filoviruses might be plant
viruses that jumped to animals for a while, just as an exercise, but since
I'm a plant virologist I always thought that I would be ridiculed. But now
that you have mentioned it, please allow me to tell you the story of a
very interesting plant virus: tomato spotted wilt virus (TSWV). 

What TSWV does to plants is analogous to what Ebola does to humans, 
although the image of a human being bleeding thru all body orifices is 
certainly more dramatic than the image of a tomato plant wilting and 
dying of generalized necrosis. 

TSWV is a member of the Bunyaviridae family, genus Tospovirus. As you 
probably know, most bunyaviruses are animal pathogens. Hantaviruses are 
also members of this family. The Tospoviruses have the same morphology 
and genomic organization of the other bunyaviruses, ie, an enveloped 
virions containing three pieces of an ambisense, ssRNA. Most viral 
proteins are also similar. However, TSWV has one *additional* gene, which 
encodes a protein that allows the virus to move systemically through the 
plant. None of the animal-infecting bunyaviruses has a similar gene. 

Some plant virologists (including this one) think that TSWV evolved from
an insect virus (it infects its vector, a species of thrips) that acquired
the extra gene via recombination, either from a plant or from another
plant virus, and then became able to infect plants. There's almost no
natural resistance to TSWV among plants, but the virus infects the insect
vector without causing any disease to it. 

The moral of this story is: couldn't it happen the other way around ?
 
Scientists have looked for the natural host of Filoviruses ad nauseum, 
with no success. Maybe it wouldn't hurt looking at some plants... 

: > Jane

: > (Who only had twenty or so Ebola messages in her mailbox.)